At present, superconducting, in particular NbTi, cables are produced from an assembly comprising a cup-shaped copper ingot, into which are inserted, in orderly manner, the ends of bars having a core of superconducting material, defined by one or a number of wires of NbTi, and a sheath of copper (and/or other noble metal). The bars are short (at most about 800 mm long), and are hexagonal in cross section to “fit” easily inside the copper ingot. The free end of the ingot is then sealed by welding on a copper cap, a vacuum is formed inside the assembly so formed, and it is subjected to one or more hot extrusion steps (at temperatures of around 500° C.) to reduce it to the size of a 60–80 mm diameter bar (of over 10 m in length). At this point, possibly after being heat treated, the bar-like semifinished product is cold drawn gradually to form a superconducting cable.
A major drawback of superconducting, particularly NbTi, cables produced as described above lies in their having a fairly low critical current (Jc) with respect to the capacity of the alloy.
The Applicant's technicians, however, have found that eliminating any hot extrusion from the processing cycle of NbTi superconductors increases critical current (Jc) by over 25% for a given chemical composition of the superconductor and for given alpha values (Cu to NbTi volume ratio of the cable).